1. Field of the Invention
The present invention relates to a master model of a lens array and a method of manufacturing the same.
2. Description of the Related Art
Recently, in the portable terminals of electronic appliances such as portable phones, PDAs (Personal Digital Assistant), or the like, small-sized and ultra-thin imaging units have been installed. These imaging units are generally provided with a solid-state imaging device such as a CCD (Charge Coupled Device) image sensor, a CMOS (Complementary Metal-Oxide Semiconductor) image sensor, or the like, and a lens for forming an image on a light sensing surface of the solid-state imaging device.
As portable terminals have become smaller and thinner and have been spread, the imaging unit installed therein has been required to become further miniaturized and thinner, along with the demands for increased productivity. For such requests, a method of mass-producing imaging units has been known, whereby a sensor array in which a plurality of solid-state imaging devices is arranged and a lens array in which a plurality of lens portions is arranged in the same manner are made to overlap each other, are combined into a single body and then the lens array and the sensor array are cut so that they include the lens portions and the solid-state imaging devices, respectively.
In manufacturing a lens array used for the above-described purpose, the following manufacturing method has been known (for example, see WO 2008/153102 corresponding to US-A-2010/0181691).
(1) Using a mold having a lens forming surface in an inverse shape of a predetermined lens surface, the shape of the lens forming surface of the mold is transferred to resin supplied onto one surface of a substrate, and then the resin is cured.
(2) By repeating the process of (1), a resin forming portion that has been formed in the shape of a lens surface is arranged on one surface of the substrate.
(3) A resin forming portion that has been formed in the shape of a lens surface is also arranged on the other surface of the substrate in the same manner to obtain a master model.
(4) An upper mold and a lower mold are obtained by accumulating metal such as Ni or the like on one surface and the other surface of the master model by an electroforming process.
(5) A photocurable resin material or a thermosetting resin material is supplied between the upper mold and the lower mold.
(6) By inserting the resin material between the upper mold and the lower mold and compressing the molds, the resin material is deformed to make along both molds.
(7) The resin material is cured by irradiating the resin material with light or heating the resin material.
According to the above-described method of manufacturing the lens array, curved surfaces formed in the shape of predetermined lens surfaces are arranged on one surface and the other surface of the master model, respectively. On the upper mold, a lens forming surface, which is in an inverse shape of the curved surface in the shape of the lens surface that is arranged on one surface of the master model, is arranged, and on the lower mold, a lens forming surface, which is in an inverse shape of the curved surface in the shape of the lens surface that is arranged on the other surface of the master model, is arranged. Also, lens portions are formed between the lens forming surfaces which are composed of a pair of the upper mold and the lower mold, and these lens portions are connected together by a substrate portion formed between the forming surfaces except for the lens forming surfaces of the upper mold and the lower mold. In the lens array used for the above-described purpose, for example, a wafer in the shape of a circular plate has a diameter of 6 inches, 8 inches, or 12 inches, as a whole, and for example, thousands of lens portions are arranged on the wafer. Hereinafter, such a lens array in particular is called a wafer-level lens array.
In manufacturing a master model of a lens array in the method of manufacturing a lens array, it is necessary to repeat the process of transferring the lens forming surfaces of molds to resin supplied onto one surface and the other surface of the substrate and curing the supplied resin for as many times as the number of lens portions arranged on the lens array. Particularly, in the case of a master model of a wafer-level lens array on which thousands of lenses are arranged, manufacturing the master model takes a very long time. Also, since resin is supplied to and formed on the substrate, a manufacturing apparatus becomes larger-scaled due to the employment of resin supply means, mold driving means, measures taken to prevent leakage of supplied resin, and the like.